MCDB 240: Fertilization I

Question 1

what is the resact gradient and why is it important?

Answer 1

resact is a protein produced by the female that diffuses around the egg; produces a gradient that is an example of chemotaxis

Question 2

describe the jelly coat of the urchin egg and how the sperm interacts with it

Answer 2

coat is made of sulfated polysaccharides; sperm has acrosome that contains digestive enzymes (bindin); jelly coat induces sperm to undergo acrosomal reaction, and actin from sperm polymerizes

Question 3

what are the parts of a sear urchin egg?

Answer 3

jelly coat –> vitelline membrane –> perivitelline space –> plasma membrane –> cortical granule

Question 4

what is the vitelline membrane?

Answer 4

coat that protects egg; occurs right after the jelly coat

Question 5

what is the plasma membrane and a special structural feature of it?

Answer 5

has many microvilli to increase surface area

Question 6

what is the perivitelline space?

Answer 6

the space b/t the vitelline membrane and the plasma membrane

Question 7

when does fertilization occur?

Answer 7

sperm and egg membrane fuse

Question 8

what is a cortical reaction (general and sea urchin?)

Answer 8

membranes of cortical granules fuse w/ plasma membrane of egg; the sperm cell unites w/ egg’s plasma membrane leading to zone pellucida modification to block polyspermy

Question 9

how does the sperm know when and where to attach to the jelly coat?

Answer 9

detects the resact gradient

Question 10

why is actin important in fertilization?

Answer 10

actin is b/t nucleus and acrosome, polymerizes, forms acrosomal filament. filament coated w/ contents of acrosome, enzymes that break down jelly coat and aid passage of sperm

Question 11

what is bindin and why is it important in species specificity?

Answer 11

bindin is an enzyme that recognizes species-specific receptors on the surface of the egg; mediates fusion of sperm and vitelline membrane?

Question 12

how contents of the sperm deposit into the egg?

Answer 12

all; nucleus, centrosomes, etc.

Question 13

what happens to the corticol granules?

Answer 13

corticol granules fuse w/ egg’s plasma membrane that are closest to sperm entry

Question 14

what are granules and why are they important when released?

Answer 14

granules are hydrolytic enzymes that degrade molecules that bind vitelline membrane to the plasma membrane; granules releases into perivitelline space

Question 15

how is the perivitelline space hydrated?

Answer 15

b/c of the release of granules; granules take up H20, therefore increasing the space between vitelline and plasma membranes

Question 16

what is the slow block?

Answer 16

vitelline membrane raises from surface of egg and makes the surface hard, preventing polyspermy; takes around 10 minutes

Question 17

what is polyspermy and how does it occur?

Answer 17

if more than one sperm fertilizes, we get more than 1 pair of centrosomes, therefore COMPLEX MITOSIS occurs, and cell will have abnormal number of chromosomes

Question 18

how are the calcium stores released?

Answer 18

fertilization triggers release of calcium stores in egg

Question 19

how is species specificity achieved?

Answer 19

acrosome reaction only occurs on contact w/ same species; bindin released during acrosomal rxn on tip of acrosomal filament

Question 20

what is fast block and what are some of the experiments/caveats?

Answer 20

sea urchins change their plasma membrane potential from -70 to 20 mV to prevent other sperm; experiment shows if you hold the resting potential at -70, polyspermy occurs.

Caveat: fast block takes a lot of energy to maintain -20 mV.